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                                                                   EXHIBIT 10.6



                 AMENDMENT NO. 4 TO LOAN AND SECURITY AGREEMENT


     AMENDMENT NO. 4, dated as of April 21, 1997, between TRANSAMERICA BUSINESS
CREDIT CORPORATION ("Lender"), and KRUG INTERNATIONAL CORP. ("Borrower") and
Borrower's wholly-owned Subsidiaries, KRUG LIFE SCIENCES INC. ("Life Sciences")
and TECHNOLOGY/SCIENTIFIC SERVICES, INC. ("TSSI") (Life Sciences and TSSI
hereinafter referred to individually as a "Borrowing Subsidiary", and
collectively as "Borrowing Subsidiaries").

     Lender and Borrower and Borrowing Subsidiaries are parties to a Loan and
Security Agreement, dated as of March 16, 1995, as amended by an Amendment No.
1 to Loan and Security Agreement dated as of September 26, 1995, and by an
Amendment No. 2 to Loan and Security Agreement dated July 16, 1996, and by an
Amendment No. 3 to Loan and Security Agreement dated as of February 10, 1997
(the "Loan and Security Agreement"). Lender, Borrower and Borrowing
Subsidiaries desire to amend the Loan and Security Agreement in certain
respects and, accordingly, the parties hereto agree as follows:

     1. DEFINITIONS. Except as otherwise provided herein, the terms defined in
the Loan and Security Agreement are used herein as defined therein.

     2. AMENDMENT. The definition of "Borrowing Base" in Section 3.1(a) of the
Loan and Security Agreement is amended and restated as follows:

     "The `Borrowing Base' shall mean, at any particular time, an amount equal
to (a) ninety percent (90%), or such other percentage as Lender, in its sole
discretion, exercised in a commercially reasonable manner, shall from time to
time consider appropriate, of Eligible Accounts - Billed, plus (b) the lesser
of (x) Four Million, Five Hundred Thousand Dollars ($4,500,000) or (y) seventy
percent (70%), or such other percentage as Lender, in its sole discretion,
exercised in a commercially reasonable manner, shall from time to time consider
appropriate, of Eligible Accounts - Estimated, provided that Lender shall give
Borrower thirty (30) days prior written notice of any change to such
percentages."

     3. REPRESENTATION AND WARRANTY. Borrower and each Borrowing Subsidiary
represents and warrants to Lender that the execution and delivery by Borrower
and each Borrowing Subsidiary of this Amendment No. 4 are within Borrower's and
each Borrowing Subsidiary's corporate power, have been duly authorized by all
necessary or proper corporate action, are not in contravention of any provision
of Borrower's or either Borrowing Subsidiary's Articles or Certificate of
Incorporation or Regulations, will not violate any law or regulation, or any
order or decree of any court or governmental instrumentality, will not conflict
with or result in the breach or termination of, constitute a default under, or
accelerate any performance required by, any indenture, mortgage, deed of trust,
lease, agreement or other instrument to which Borrower or either Borrowing
Subsidiary is a party or by which Borrower or either Borrowing Subsidiary or
any of its property is bound and do not require the consent or approval of any
governmental body, agency, authority or any other person.

     4. NO DEFAULT. Borrower and each Borrowing Subsidiary represents and
warrants that no Default or Event of Default exists as of the date hereof.


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     5. MISCELLANEOUS. Except as herein provided, the Loan and Security
Agreement shall remain unchanged and in full force and effect. This Amendment
No. 4 may be executed in any number of separate counterparts, each of which
shall, collectively and separately, constitute one agreement. This Amendment
No. 4 and the obligations arising hereunder shall be governed by, and construed
and enforced in accordance with, the laws of the State of Illinois applicable
to contracts made and performed in such state, without regard to the principles
thereof regarding conflict of laws, and any applicable laws of the United
States of America.

     IN WITNESS WHEREOF, this Amendment No. 4 has been duly executed as of the
day and year specified at the beginning hereof.

TRANSAMERICA BUSINESS CREDIT              KRUG INTERNATIONAL CORP.
CORPORATION

By:                                       By:
   ---------------------------------         ----------------------------------
   Name:                                     Name:
         ---------------------------                ---------------------------
   Title:                                    Title: 
         ---------------------------                ---------------------------


                                          KRUG LIFE SCIENCES INC.

                                          By:     /s/ Robert M. Ellis
                                             ----------------------------------
                                             Name:      Robert M. Ellis
                                                    ---------------------------
                                             Title:     Vice President
                                                    ---------------------------


                                          TECHNOLOGY/SCIENTIFIC
                                          SERVICES, INC.

                                          By:
                                             ----------------------------------
                                             Name:
                                                    ---------------------------
                                             Title:
                                                    ---------------------------




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